Due to the huge pressure of energy saving and environmental protection, energy-saving and environment-friendly products are developed in many automobile industries around the world. For example, a Chinese patent application No. CN102700407A has proposed an electrically-controlled 2-speed automated mechanical transmission (AMT) for a pure Electric Vehicle (EV). This 2-speed automated mechanical transmission has an advantage of high power transmission efficiency, without power interruption during shifting. Besides, compared with a pure electric vehicle with a single-speed transmission, the electric vehicle with such 2-speed automated transmission has been improved greatly in performances such as acceleration, grade ability and energy consumption economy.
However, due to the restriction of battery technologies, the driving range of the pure electric vehicle still cannot meet the demand for long-distance driving. The Hybrid Electric Vehicle (HEV), which is advantageous for an unchanged infrastructure, relatively mature technologies used and less pollution, has become a realistic option to solve energy and environment problems presently.
A Chinese patent application No. CN102490588A discloses a plug-in hybrid power driving mechanism, which employs two electric motors and one engine as power sources, to effectively utilize high-efficiency operation areas of the motors and engine. However, these two motors increase costs, thus such hybrid power driving mechanism is suitable for only business vehicles and multifunctional sport vehicles which are demanding for high power.